R-366 slice 2 (decision 168): the host report carries the archives the restore-test skipped as another key's

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0159rPz1ZhFKsS53msqPYxtS

internal/backup/foreign_key_ledger.go

@@ -0,0 +1,60 @@
+package backup
+
+import (
+	"context"
+	"sort"
+	"sync"
+	"time"
+
+	"gitea.dooplex.hu/admin/felhom-agent/internal/hub"
+)
+
+// ForeignKeyLedger (R-366 slice 2, `09` §3 decision 168) holds, per backup tier, the whole-guest archives the
+// restore-test pick skipped because another key wrote them (R-727 — an earlier install of this box). Since R-727 the
+// skip was one INFO log line per archive and nothing else, so after a reinstall the operator was never told that the
+// box's older whole-guest copies are unreadable to it. The host report carries this ledger; the hub raises ONE
+// operator event when it changes.
+//
+// It reports nil until a tier has been evaluated since the agent started, so a restart does not read as "the set
+// changed to empty" (the hub keeps its last state for an absent field).
+type ForeignKeyLedger struct {
+	mu       sync.Mutex
+	byTarget map[string]hub.ForeignKeyArchives
+}
+
+// NewForeignKeyLedger builds an empty ledger.
+func NewForeignKeyLedger() *ForeignKeyLedger {
+	return &ForeignKeyLedger{}
+}
+
+func (l *ForeignKeyLedger) set(target string, n int, oldest, newest int64) {
+	l.mu.Lock()
+	defer l.mu.Unlock()
+	if l.byTarget == nil {
+		l.byTarget = map[string]hub.ForeignKeyArchives{}
+	}
+	e := hub.ForeignKeyArchives{Target: target, Count: n}
+	if n > 0 {
+		e.Oldest = time.Unix(oldest, 0).UTC().Format(time.RFC3339)
+		e.Newest = time.Unix(newest, 0).UTC().Format(time.RFC3339)
+	}
+	l.byTarget[target] = e
+}
+
+// ForeignKeyArchives implements hub.ForeignKeyArchiveReporter: nil before any evaluation; otherwise the tiers that
+// hold such archives (`Tiers` empty, never nil, when none do), sorted by tier.
+func (l *ForeignKeyLedger) ForeignKeyArchives(context.Context) *hub.ForeignKeyArchivesStanza {
+	l.mu.Lock()
+	defer l.mu.Unlock()
+	if l.byTarget == nil {
+		return nil
+	}
+	out := []hub.ForeignKeyArchives{}
+	for _, e := range l.byTarget {
+		if e.Count > 0 {
+			out = append(out, e)
+		}
+	}
+	sort.Slice(out, func(i, j int) bool { return out[i].Target < out[j].Target })
+	return &hub.ForeignKeyArchivesStanza{Tiers: out}
+}